Reminder: Donald Trump is the president of the United States, the head of the US military and, arguably, the single most powerful person in the world.

O'Donnell and Trump have a loooooong history -- dating all the way back to 2006. Trump refused to de-crown (not sure that's a word) Miss USA Tara Conner after reports of her past alcohol and drug use surfaced. O'Donnell, at the time a co-host of "The View," blasted Trump the following day -- calling him "a snake-oil salesman on Little House On The Prairie" among many other things.

O'Donnell came up in the general election as well. In the first debate of the general election, Hillary Clinton raised the same Trump comment about women as "fat pigs, dogs, slobs, disgusting animals." Trump responded: "Rosie O'Donnell, I said very tough things to her and I think everyone would agree that she deserves it and nobody feels sorry for her."

O'Donnell, for what it's worth, has given as good as she has gotten.

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Rosie O'Donnell reignites feud with Donald Trump?

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But, only one of these two people are president of the United States. Only one of them is making decisions about sending missiles into a Syrian airfield or dropping the "mother of all bombs" on Afghanistan. Or making final calls on the number of troops in Afghanistan. Or developing tax policy and trade policy with far-reaching impacts on the US economy. Or representing the US on the world stage.

On Thursday, O'Donnell responded: "u don't even realize the kind of trouble u r in - comeys people believe in him - for real - they have the proof - u r a sadistic man #USA"

@realDonaldTrump - u don't even realize the kind of trouble u r in - comeys people believe in him - for real - they have the proof - u r a sadistic man #USA

Now, it's easy to laugh at Trump's decision to re-engage his long-simmering feud with O'Donnell. (It's a good tweet and an expert troll, after all.)

But, it should also give everyone pause. This is the president of the United States we are talking about. (I know I have said that three times. But it bears repeating!) He -- and his administration -- are in the midst of a self-inflicted crisis over the reasons for his decision to fire Comey. That he made time to troll Rosie O'Donnell says something about where his priorities and focus lie. And what it says is nothing good.